Process and device for vaporizing a liquid by heat exchange with a second fluid and their application in an air distillation installation

ABSTRACT

Liquid oxygen of a low pressure column forms a bath 5 at the top of a heat exchanger 2 of the type having plates defining vertical passages 17, 18. This liquid is predistributed along every other passage 17 by a series of apertures 27 formed for example in the plates, and then is uniformly distributed in a fine manner in the same passages by a packing 24 so as to form a continuous running liquid film. The gaseous nitrogen of a medium pressure column is introduced into the remaining passages 18 and condensed by heat exchange with the oxygen which is vaporized.

The present invention relates to the vaporization of a liquid by heatexchange with a second fluid by means of a heat exchanger of thevertical plate type. It is in particular applicable to air distillationinstallations.

In air distillation installations of the type having a double column,the liquid oxygen in the bottom of the low pressure column is vaporizedby heat exchange with gaseous nitrogen taken from the head of the mediumpressure column. For a given operating pressure of the low pressurecolumn, the temperature difference between the oxygen and the nitrogenrendered necessary by the structure of the heat exchanger imposes theoperating pressure of the medium pressure column. It is thereforedesirable to arrange that this temperature difference be as small aspossible so as to minimize costs related to the compression of the airto be treated injected into the medium pressure column.

For this purpose, it has been proposed to supply the heat exchanger withliquid oxygen from the upper end by ensuring the running of this liquidalong tubes of great length (up to about 6 m).

Remarkable performances have been achieved in this way from the heatexchange point of view, but at the cost of serious technicaldifficulties. Indeed, in particular when large flows of oxygen must betreated, problems are encountered in the construction of a multitude oflong tubes resisting the exterior pressure of the nitrogen and otherproblems are encountered which are related to the presence of thickstainless steel end plates.

An object of the invention is to provide means for achieving heatexchange performances which are at least just as good but in a morereliable and cheap manner.

The invention therefore provides a process for vaporizing a liquid byheat exchange with a second fluid by means of a heat exchangercomprising a parallelepipedal body formed by an assembly of parallelvertical plates defining therebetween a multitude of flat passages, saidprocess being of the type in which the liquid is sent into a first groupof passages and the second fluid is sent into the remaining passages,characterized in that it comprises distributing the liquid in two stagesat the upper end of the passages of said first group throughout thehorizontal length of the last mentioned passages, the two stagescomprising a rough predistribution of the liquid throughout the lengthof the passages of said first group, then a fine distribution throughoutthe length of these passages of the thus predistributed liquid.Preferably, the supply of liquid is adapted to ensure permanently thepresence of a liquid film on substantially the entire extent of thewalls contained in each of the passages of said first group.

The invention also provides a heat exchanger for carrying out such aprocess. This exchanger comprises means for predistributing the liquidopening onto means for effecting a fine distribution of the liquidlocated at the upper end of each of the passages of said first group.

In a particularly effective embodiment of the exchanger according to theinvention, the predistribution means comprise in particular a horizontalrow of apertures, and retaining means for forming a bath of liquid abovethese openings; the fine distribution means may comprise a packing, or,when said openings are provided in the plates of the exchanger, asurface for spreading the jets of liquid issuing from these openings.

The invention also provides an air distillation installation of the typehaving a double column, in which the liquid of the bottom of the mediumpressure column is put into thermal exchange relation with the gas ofthe head of the low pressure column by means of a heat exchanger of thetype defined hereinbefore, said installation comprising supply means forsupplying the liquid to said predistribution means and means supplyinggas to the passages of said second group.

Several embodiments of the invention will now be described withreference to the accompanying drawings. In these drawings:

FIG. 1 is a partial diagram of an air distillation installationaccording to the invention;

FIG. 2 is a partial diagrammatic perspective view, with a part cut away,of a heat exchanger used in the installation shown in FIG. 1;

FIG. 3 is a similar view of a modification of the heat exchanger shownin FIG. 2;

FIGS. 4 and 5 are respectively perspective views of two modifications ofa detail of the exchanger shown in FIG. 3;

FIG. 6 is a partial perspective view, with parts cut away, of anotherheat exchanger according to the invention;

FIG. 7 is a diagrammatic sectional view of a part of a heat exchangeraccording to another embodiment of the invention; and

FIG. 8 is a similar view of a modification of the exchanger shown inFIG. 7.

In the various embodiments which will be described hereinafter, the samereferences will designate identical or corresponding elements.

FIG. 1 illustrates a possible incorporation of an oxygen-nitrogen heatexchanger in an air distillation installation having a double column.This installation comprises a medium pressure column 1 at the base ofwhich the air to be treated is injected at a pressure of the order of 6bars (absolute). The liquid enriched with oxygen which is collected atthe bottom of the column 1 is refluxed in the middle of the height of asecond column (not shown) termed a low pressure column, which operatesslightly above atmospheric pressure. The gaseous nitrogen located at thehead of the column 1 is put into heat exchange relation with the liquidoxygen collected at the bottom of the low pressure column; the resultingcondensed nitrogen serves as a reflux in the column 1 and the lowpressure column, while the resulting vaporized oxygen is sent to thebottom of the low pressure column.

The heat exchange between the oxygen and the nitrogen occurs in anexchanger 2 which is mounted above the column 1, while the low pressurecolumn is in juxtaposed relation to the latter.

The exchanger 2 is formed by a fluidtight case 3 the essential part ofthe height of which contains an assembly of parallel plates 4 ofaluminum having a rectangular shape, a length of the order of 1 to 1.5 mand a height of 3 to 6 m, between which corrugations also of aluminiumare fixed by brazing.

The space located above the plates 4 encloses a bath of liquid oxygen 5supplied through a pipe 6 coming from the bottom of the low pressurecolumn and provided with a pump (not shown). The latter may becontrolled by a level regulator of the bath 5 which has beendiagrammatically represented by a level measuring tube 6A, or, by way ofa modification, by a flow regulator. Provided at the top of theexchanger 2 is a pipe 7 for returning to the base of the low pressurecolumn oxygen vaporized above the bath 5, resulting from entries of heatin the region of the pump and the piping.

The assembly of plates 4 is supplied in its upper part with gaseousnitrogen through a horizontal feed box 8 which communicates through apipe 9 with the head of the medium pressure column 1. The condensednitrogen is discharged at the base of the plates 4 by a horizontalcollector box 10 which communicates through a pipe 11 with a liquidsealed trough 12 disposed at the head of column 1. Connected to the box10 is a pipe 13 for discharging uncondensable rare gases.

A pipe 14 connects the bottom of the low pressure column to the space inthe case 3 below the plates 4. This pipe extends vertically into thisspace through the lower point of the case 3 and its upper end issurmounted by a conical deflector 15. Extending from the bottom of thecase 3 is also a pipe 16 for returning excess liquid oxygen to thebottom of the low pressure column.

The structure of the active part of the exchanger 2, i.e. the assemblyof plates 4, will now be described with reference to FIG. 2.

In this region of the exchanger the case 3 has a parallelepipedal shape.The plates 4 define a multitude of passages alternately for the flow ofoxygen (passages 17) and for the flow of nitrogen (passages 18). In themajor part of their height, the passages 17 and 18 each contain acorrugation or wave 19 formed by a perforated aluminum sheet corrugatedwith vertical generatrices.

The corrugations 19 of the nitrogen passages terminate both at the topand the bottom before the corrugations 19 of the oxygen passages. At thebase of the plates 4, these corrugations of the passages 18 are extendedby oblique corrugations for collecting nitrogen (not shown) which leadto the entrance of the collector box 10. At their upper end, thesecorrugations 19 are extended by nitrogen distributing obliquecorrugations 20 which open onto the outlet of the feed box 8. Above thecorrugations 20, the nitrogen passages 18 are closed by horizontal bars21. Similar bars close the lower end of the nitrogen passages below thenitrogen collecting zones. Above the bars 21, each nitrogen passagecomprises a liquid oxygen reservoir 22 containing a vertical corrugation23 which is made from perforated aluminum sheet and has verticalgeneratrices, the thickness and the pitch of which are distinctlygreater than those of the corrugations 19. The corrugations 23 have forsole function to provide spacing means between the plates 4 so as topermit the assembly of the exchanger by a single brazing operation. Thereservoirs 22 are open in the upper part so as to communicate with theliquid oxygen bath 5. The corrugations 19 of the oxygen passages 17extend downwardly to the lower end of the plates 4 so that thesepassages are downwardly open. These corrugations extend upwardly to theupper edge of the bars 21 and then are extended by a lining 24. Thelatter is formed by a corrugation of the "serrated" type which isillustrated in more detail in FIG. 6.

As shown in FIG. 6, the corrugation 24 is a non-perforated aluminumsheet having horizontal generatrices (arrangement termed "hard way"relative to the flow of the liquid oxygen). At regular intervals, eachhorizontal or pseudo-horizontal face 25 of the corrugation 24 isprovided with a sheared portion 26 which is upwardly offset by a quarterof a corrugation pitch. The width of the sheared portions 26, measuredalong a generatrix of the corrugation, is of the same order as thedistance between each one thereof and two adjacent sheared portionslocated on the same face 25.

Returning to FIG. 2, each plate 4 comprises above the packing 24, ahorizontal row of apertures 27 evenly spaced apart throughout the lengthof the exchanger, the apertures of successive plates being disposed atthe same height but in staggered relation. By way of a modification,these apertures could be moreover provided only in every other plate.Just above these apertures, the oxygen passages are closed by horizontalbars 28 disposed at the upper end of plates 4. In order to avoid risk ofobstruction of certain apertures 27 by the corrugations 23, the latterare interrupted on a short height in the region of said apertures.

In operation, the device regulating the feed pump feeding liquid oxygento the exchanger 2 maintains a level of the bath 5 above the plates 4which is sufficient to overcome the various pressure drops which opposethe flow of oxygen. The head of liquid oxygen above the plates 4 is forexample of the order of 20 cm.

The liquid oxygen fills the reservoirs 22 and passes through theapertures 27 at a rate of flow defined by the section of these aperturesand by the liquid head thereabove. As this head is constant in anestablished operation, the flow of liquid oxygen is that delivered bythe pump raising this liquid. The apertures 27 therefore effect a roughpredistribution of the liquid oxygen all along the passages 17, and theliquid oxygen predistributed in this way reaches the packing 24 whichensures a fine distribution throughout the length of each passage 17.The liquid oxygen thus reaches the corrugations 19 by running in aperfectly uniform manner along all the walls (corrugations 19 and plates4) of the passages provided therefor, i.e. by forming a continuousdescending film on these walls.

At the same time, the gaseous nitrogen reaches the exchanger through thebox 8 and the distribution corrugations 20, then flows downwardly alongthe passages 18. In doing so, it progressively gives up heat to theliquid oxygen located in the adjacent passages 17 so that the oxygen isvaporized and the nitrogen is simultaneously condensed.

The condensed nitrogen is collected in the box 10 and flows in the pipe11 to the channel 12. When the head of liquid nitrogen in the pipe 11 issufficient to overcome the pressure prevailing in the medium pressurecolumn 1, this liquid overflows the channel and is refluxed in themedium pressure column after a part has been taken off through the pipe11A to ensure the refluxing of the low pressure column. A suction iscreated in this way in the passages 17 which ensures the circulation ofthe nitrogen.

The flow of liquid oxygen is so regulated as to guarantee an excess ofliquid oxygen throughout the height of the plates 4. Indeed, a totalvaporization of the oxygen in the region of the passages 17 would resultat this place in a concentration of acetylene dissolved in the liquidoxygen which could cause a local explosion. Apart from this risk ofexplosion, a lower performance of the exchanger would also result owingto the neutralization of the non-wetted surface. This risk is limited bythe high effectiveness of the fine distribution ensured by the packing24. However, for reasons of safety, it is preferred to employ an excessof liquid oxygen, usually of the same order as the vaporized oxygenflow.

Consequently, a diphase gaseous oxygen-liquid oxygen mixture issues fromthe lower end of the passages 17; this mixture is separated in the lowerpart of the case 3, the liquid and vapour phases returning respective tothe bottom of the low pressure column through the pipes 16 and 14.

The applicant has found that such an exchanger can operate in aperfectly reliable manner with a very small temperature difference, ofthe order of 0.5° C., between the nitrogen and the oxygen, whichconsequently enables the air entering the distillation installation tobe compressed under very economical conditions.

In the embodiment shown in FIG. 2, it can be seen that the liquid oxygenis entirely distributed when the fluid arrives in the zone of heatexchange with the nitrogen. In the modification shown in FIG. 3, on theother hand, the oxygen is put into thermal exchange relation with thenitrogen right at the start of the fine distribution operation.

For this purpose, the bars 21 which provide the upper limit of thepassages 18 are disposed at the upper end of the plates 4, as are thebars 28. Further, the apertures 27 are eliminated and replaced byvertical apertures 29 provided in evenly spaced relation in the bars 28,throughout the length of the latter.

In this modification, the liquid oxygen of the bath 5 flows through theapertures 29 at a rate of flow corresponding to the output of the liquidoxygen raising pump and is thus predistributed throughout the length ofthe passages 17. These liquids then fall onto the packing 24 locatedjust below (this packing has been shown very diagrammatically in FIG.3). As before, the packing 24 ensures a uniform fine distribution of theliquid oxygen throughout the length of passages 17, and this liquidthereafter runs along the corrugations 19 and the coresponding walls 4.The heat exchange between the oxygen and the nitrogen starts during thepassage of the liquid oxygen through the packings 24, which are at thesame level as the corrugations 20 distributing gaseous nitrogen.

As illustrated in FIG. 4, the apertures 29 of the bars 28, instead ofhaving a constant diameter throughout the height of these bars, may havea diameter enlarged in the major part of their height by a counter bore29A effected from below.

FIG. 5 shows that similar apertures may be obtained by perforation ofthe upper web 30 of U-section elements constituting the bars 28. Theadvantage of these two embodiments resides in the fact that theeffective part of the apertures 29 which defines the section for thepassage of the liquid oxygen is of short length and consequently lesssubject to stopping up or undesirable vaporization.

In the heat exchangers shown in FIGS. 2 and 3, the vaporized oxygen isdischarged through the base at the same time as the excess liquidoxygen. In this embodiment shown in FIG. 6, on the other hand, thevaporized oxygen is free to be discharged from both the top and bottom.

The exchanger shown in FIG. 6 is identical to that of FIG. 2, from thebase of the plates 4 up to the level of the upper edge of the bars 21which define the upper limit of nitrogen passages 18.

Just above these bars 21, each plate 4 has a horizontal row of apertures31. Above the latter, the plates 4 extend for a great height up to alevel higher than that of the free surface of the liquid oxygen bath 5.Disposed in the gaps above the bars 21 are corrugated spacer elements 32having vertical generatrices similar to the corrugations of FIG. 2. Inthe remaining gaps, a free space 33 is provided in the region of theapertures 31 above the corrugations 19, and this space is surmountedupwardly by the previously-described packing 24, by a bar 28 havingapertures 29 similar to those of FIG. 3, and by a corrugated spacerelement 34 similar to the elements 32 but having horizontalgeneratrices.

The bath 5 is fed laterally by a feed box 35 located above the box 8 andopening into the spaces occupied by the corrugations 34. For thispurpose, the bars 36 which close on this side the oxygen passages 17extend upwardly only up to the level of the upper edge of the bars 28.

In operation, a suitable constant liquid oxygen level is maintained inthe box 35. The bath 5 rises above the bars 28 and, as in FIG. 1, theliquid oxygen flows through the apertures 29 in packing 24 whichdistributes it in a fine and uniform manner, then the liquid runs in thepassages 17 in heat exchange relation with the nitrogen contained inpassages 18. The vaporized oxygen can be discharged either downwardly asbefore, or upwardly by passing through the apertures 31 and the spacescontaining the corrugations 32, as indicated by the arrows in FIG. 6.

In this embodiment, by way of a modification, the passages 17 may alsobe closed at their lower end and receive the liquid oxygen by means ofan oblique collector corrugation and a horizontal collector boxconnected by a pipe to the liquid oxygen bath at the bottom of the lowpressure column. In this case, the entire vaporized oxygen issues fromthe exchanger through the top in the manner described hereinbefore.

The heat exchanger illustrated in FIG. 7 differs from that shown in FIG.2 only in the manner in which the oxygen is distributed and discharged.In each passage 17, the packing 24 is eliminated; the jets of liquidoxygen 37 issuing from the apertures 27 strike the confronting plate 4and spread over the latter. The spacing and the diameter are so chosenthat the sheets of parabolic shape thus formed join into a continuoussheet a little above the thermal exchange corrugations 19. Thus, theoxygen is still predistributed by the apertures 27 while its finedistribution is ensured by the plates 4 themselves.

This manner of distribution is particularly simple and has the advantageof avoiding the creation of a large obstacle to the discharge of thevaporized oxygen through the upper end of the passages 17, asillustrated. The lower end of the passages 17 may then be either closedand provided with means for collecting the excess of liquid oxygen, oropen so as to allow the gaseous oxygen also the possibility of beingdischarged from below.

In order to improve the spreading of the liquid oxygen jets on the plate4, the surface condition of the latter may be locally modified, inparticular by preferably horizontal ribbing, and/or by the provision ofa horizontal obstacle 38 projecting from this plate above the jets, asshown in dotted lines. The improvement in the spreading of the jetspermits, for a given rate of flow, the use of larger apertures 27 in asmaller number so that the risk of a stopping up of these apertures byparticles in suspension in the liquid is reduced.

By way of a modification (FIG. 8) the zones for spreading the jets maybe provided on additional plates 39 mounted on the plates 4.

The region of the exchanger located above the bars 21 requires nocorrugation. For the purpose of assembling the exchanger by brazing,there may be disposed in this region, between the plates 4, spacerblocks which are thereafter removed, the plates 39 being if desiredmounted subsequently. In another modification, as represented, there maybe employed as spacer members corrugations 23 made from a thick sheetand having a large pitch; these corrugations being interrupted at thelevel of the apertures 27 and in the jet spreading zones. In FIG. 8,there has been shwon in the passages 17 a corrugation 23 in two parts,respectively above and below the apertures 27, with a ribbed zone 40facing these apertures and another ribbed zone 41 between thecorrugation 23 and the corrugation 19. This FIG. 8 moreover shows thatsuch corrugations 23 enable the additional plates 39 to besimultaneously placed in position.

By way of a modification, apertures 27 may be provided in all the plates4, with of course a suitable offset so as to supply each passage 17 withtwo sheets of liquid oxygen.

In each embodiment of the exchanger according to the invention, thenitrogen circuit is conventional. It can therefore be replaced by otherknown types of nitrogen circuits and in particular by those disclosed inthe French Pat. No. 78 20,757 of the applicants' assignee.

Further, one or more heat exchangers according to the invention may beinstalled inside a double column of an air distillation installationwhose low pressure column is superimposed on the medium pressure column.

What is claimed is:
 1. A process comprising vaporizing a liquid by heatexchange with a second fluid by means of a heat exchanger designed tomaintain no more than a small temperature difference between said liquidand said second fluid, including a parallelepipedal body formed by anassembly of parallel vertical plates defining therebetween a multitudeof flat passages having generally vertical corrugated fins therein, bysending said liquid into a first group of said passages and sensing thesecond fluid into a second group of passages constituting the remainingpassages of said passages defined between said plates, distributing theliquid in two stages at an upper end of the passages of said first groupof passages throughout the horizontal length of said first group ofpassages, said two stages comprising a rough predistribution of theliquid .Iadd.through openings .Iaddend.throughout the length of passagesof said first group of passages, and then a fine distribution of thethus predistributed liquid .Iadd.through a packing .Iaddend.throughoutthe length of said passages, the two stages being performed above anupper end of said generally vertical corrugated fins.
 2. A processaccording to claim 1, comprising adapting the liquid flow in such manneras to ensure permanently the presence of a liquid film on substantiallythe entire extent of all the walls contained in each of the passages ofsaid first group of passages.
 3. A process according to claim 1,comprising constraining the gas resulting from the vaporization of theliquid and the liquid in excess to leave the exchanger from the bottomof the exchanger.
 4. A process according to claim 1, comprising takingthe liquid from a bath of liquid provided at the top of the exchanger.5. A process according to claim 4, wherein said bath of liquid is at aregulated level.
 6. A process according to claim 4, wherein the passagesof said first group of passages are put in communication with a freespace located above the bath of liquid.
 7. A process according to claim1, comprising sending into said first group of passages an excess ofliquid of the same order as the flow of vaporized liquid.
 8. A processaccording to claim 1, wherein the liquid is liquid oxygen and the secondfluid is gaseous nitrogen in the course of condensation.
 9. A heatexchanger comprising means designed for vaporizing a liquid by heatexchange with a second fluid while maintaining no more than a smalltemperature difference between said liquid and said second fluid, saidexchanger including a parallelpipedal body including an assembly ofparallel vertical plates having walls defining therebetween a multitudeof flat passages having generally vertical corrugated fins therein, saidpassages comprising a first group of said passages and a second group ofpassages constituting the remainder of said passages defined by saidwalls of said plates, means .Iadd.defining openings .Iaddend.foreffecting a rough predistribution of the liquid, means .Iadd.comprisinga packing .Iaddend.for effecting a fine distribution of the liquid, themeans for effecting the predistribution of the liquid opening onto saidmeans for effecting the fine distribution of the liquid which aredisposed at an upper end of each of the passages of said first group ofpassages, both said means being disposed above an upper end of saidgenerally vertical corrugated fins.
 10. A heat exchanger according toclaim 9, .[.wherein the predistribution means comprise means definingopenings,.]. and retaining means for forming a bath of liquid above saidopenings.
 11. A heat exchanger according to claim 10, wherein saidopenings are formed by a horizontal row of apertures.
 12. A heatexchanger according to claim 10, wherein said retaining means comprisebars limiting the passages of said second group of passages at the upperend thereof at a given distance from the upper end of the verticalplates, said openings being provided in the plates above said bars. 13.A heat exchanger according to claim 12, wherein, for the purpose ofputting the passages of said first group of passages in communicationwith a free space located above the bath of liquid, means are providedfor putting a region of the passages of said first group of passageslocated below the fine distribution means in communication with the freespace located above the bath of liquid, said plates extending to abovethe level of the bath of liquid, additional bars upwardly limiting thepassages of said second group of passages, and said communication meanscomprising openings formed in said plates above said additional bars andbelow said fine distribution means. .[.14. A heat exchanger according toclaim 12, wherein said fine distribution means comprise a surface forspreading jets of liquid issuing from said openings..]. .[.15. A heatexchanger according to claim 14, wherein said spreading surface isribbed..]. .[.16. A heat exchanger according to claim 15, wherein saidspreading surface is ribbed horizontally..]. .[.17. A heat exchangeraccording to claim 14, wherein said spreading surface carries aprojection located above the jets of liquid..].
 18. A heat exchangeraccording to claim 10, wherein said retaining means comprise barslimiting the passages of said first group of passages at the upper endthereof, said openings being formed vertically in said bars.
 19. A heatexchanger according to claim 18, wherein each opening is formed by acounter-bored aperture.
 20. A heat exchanger according to claim 18,wherein each bar is an inverted U-section element having a webinterconnecting two branches of the U, and a series of apertures isprovided in said web.
 21. A heat exchanger according to claim .[.18.]..Iadd.9.Iaddend., wherein the packing comprises a corrugation havinghorizontal generatrices and a partial vertical offset.
 22. A heatexchanger according to claim 10, wherein, for the purpose of putting thepassages of said first group of passages in communication with a freespace located above the bath of liquid, means are provided for putting aregion of the passages of said first group of passages located below thefine distribution means in communication with the free space locatedabove the bath of liquid. .[.23. A heat exchanger according to claim 9,wherein said fine distribution means comprise a packing..].
 24. A heatexchanger according to claim 9, wherein said fine distribution means aredisposed at the same level as a device for distributing the second fluidin the passages of said second group of passages.
 25. A heat exchangeraccording to claim 9, wherein said fine distribution means are disposedentirely above a device for distributing the second fluid in thepassages of said second group of passages.
 26. An installation forseparating air by distillation, said installation comprising a firstdistillation column operating at a relatively high pressure, a seconddistillation column operating at a relatively low pressure, and a heatexchanger for putting the liquid of the bottom of the second column inthermal exchange relation with the gas of the head of the first column,said heat exchanger comprising means designed to vaporize a liquid byheat exchange with a second fluid while maintaining no more than a smalltemperature difference between said liquid and said second fluid andincluding a parallelepipedal body including an assembly of parallelvertical plates having walls defining therebetween a multitude of flatpassages having generally vertical corrugated fins therein, saidpassages comprising a first group of said passages and a second group ofsaid passages constituting the remainder of said passages defined bysaid walls of said plates, means .Iadd.defining openings .Iaddend.foreffecting a rough predistribution of the liquid, means .Iadd.comprisinga packing .Iaddend.for effecting a fine distribution of the liquid, themeans for effecting the predistribution of the liquid opening onto saidmeans for effecting the fine distribution of the liquid which aredisposed at an upper end of each of the passages of said first group ofpassages, both said means being disposed above an upper end of saidgenerally vertical corrugated fins, supply means for supplying theliquid to said predistribution means, and means for supplying gas to thepassages of said second group of passages.
 27. An installation accordingto claim 26, wherein said supply means comprise means for creating abath of liquid at the top of the exchanger.
 28. An installationaccording to claim 27, wherein said supply means comprise means forregulating the level of said bath of liquid. .Iadd.29. An installationaccording to claim 26, wherein said openings are adapted to supply anexcess flow rate of said liquid which is of the same order as a flowrate of said liquid which is vaporized in said heat exchanger. .Iaddend.